Fuse blowing

ricnor · #1 08-22-2006, 06:05 AM

My 97 454 burb suddenly cut out when driving, leave it for a while and it would start up again for a few more miles and then cut out again. Now it is blowing a 20 amp fuse that is for the ECM-B. When it blows it stops the power to the fuel pump relay. Now it won't go at all as the fuse blows every time I try it.
What is the ECM-B anyway and can it short out to blow fuses or is it a wire that is arcing to earth. Any help much appreciated.

777stickman · #2 08-22-2006, 11:44 AM

ECM B fuse supplies a constant 12v (hot at all times) to the VCM/PCM and to the fuel pump relay. The fuse is blowing telling you that there is a direct short to ground somewhere. Try this, take the fuel pump relay out and put a new fuse in. If it doesn't blow put the relay back in and if it blows then try a new relay. The relay may be shorted to ground internaly. Other wise you'll have to trace the wires to the VCM and the pump relay to look for a chafed wire that's contacting metal. The wire coming from the ECM B fuse is orange and has a splice in it going to the pump relay and the VCM/PCM.
Hope this helps..............Steve

ricnor · #3 08-23-2006, 09:15 AM

Steve, Thanks for your imput. I have done as you suggested and find that the fuse blows only when the engine has warmed up (so could get about 3 miles from cold) and continues to blow only when I crank the engine over to start and only when the fuel pump relay is installed. Take the relay out and I can crank the engine for ages and the fuse will be ok.
I will order an new relay and see what happens. (could take a while as no-one stocks this sort of item over here so will be special order).
Again thanks for the imput and I'll let you know how it goes.
Regards, Paul.

Old Dave · #4 08-23-2006, 09:43 AM

You might check in the the compartment where the fuel pump relay to see if you have another relay that is the same that runs something else. You could swap them and see if it's really the relay before you order one and have to wait on it.

777stickman · #5 08-23-2006, 10:58 AM

Paul: Your 2nd description leads me in another direction. When the car is started the pump relay directs the 12v power from the ECM-B fuse to the fuel pump. I'm now thinking the pump itself or the wiring to the pump is faulty causing a very high resistance which is blowing the fuse. Definitaly try what "old dave" suggests before ordering a new relay........Steve

ricnor · #6 08-23-2006, 04:52 PM

Thanks for the idea "old Dave" but unfortunately the only other two relays are 4 pin affairs and the fuel relay is a 5 pin item so can't try that one. Is there anyway that I can bypass the relay alltogether to see if the fuse continues to blow? I have located the feed to the relay and the outlet power from the relay but have no idea what the other three connectors are for.
New relay will be two weeks and about $50, having said that I have a couple of more places to try tomorrow that may actually stock them on the shelf. If I can't sort it out myself I may have to take it to an auto electrician but am really loath to do so as they don't know much about american vehicles over here and most of their input will be guesswork. Thanks to both of you for trying so far, if the weather is fine tomorrow I will see if I can trace the wiring back to the pump and check for any shorts.

777stickman · #7 08-23-2006, 06:20 PM

Paul: The 4 pin relay will work for the purpose of trouble shooting. The 5th pin on the pump relay is for a pump prime connector. Try the A/C relay and let us know what happens. The other three connectors are for the prime circuit (red wire), the relay control signal from the VCM (dk grn/wht wire) and the ground for the relay control signal (blk/wht wire).............Steve

Old Dave · #8 08-24-2006, 08:35 AM

Steve:
Couldn't Paul bypass the relay by taking a jumper wire with an INLINE3 15A FUSE and put power on the relay socket that switches 12V to the pump? This would tell him if it's something down stream or the relay itself. If the fuse blows it's either the vehicle wiring from the relay socket back or the pump itself.

777stickman · #9 08-24-2006, 11:24 AM

Quote:

Originally Posted by Old Dave

Steve:
Couldn't Paul bypass the relay by taking a jumper wire with an INLINE3 15A FUSE and put power on the relay socket that switches 12V to the pump? This would tell him if it's something down stream or the relay itself. If the fuse blows it's either the vehicle wiring from the relay socket back or the pump itself.

You bet Dave. Take the pump relay out and look by the pins on the relay for very small numbers. 85, 86, 87, 87a & 30. Match up # 87 & #30 in the relay socket and jumper those two. Sould be the Orange and Gray wires. Keep in mind that this will cause the fuel pump to run constantly even with the key off.

Steve

ricnor · #10 08-24-2006, 06:15 PM

Only just managed to get on the computer and it's now 2300hours here so have only just read your other suggestions, however, I did as you suggested earlier and used the A/C relay. The Burb ran from cold and then died as before, the fuse had not blown at this point. I then cranked the engine to try to restart and the fuse blew instantly. I'll give bypassing the relay altogether a go tomorrow.
Could the choke/fuel enrichment system have anything to do with the problem. It appears that the engine is fine from cold but when the choke should cut off the engine dies and then the fuse blows when the engine is cranked over.
I was also thinking of waiting for it to happen again and then disconnect the fuel pump and see if the fuse blows when cranked over, this would possibley eliminate the pump if it continues to blow.
On the plus side I don't have to wait two weeks for a new relay.
Again thanks to both of you, your thoughts are most appreciated.

777stickman · #11 08-24-2006, 08:20 PM

Paul: I think you should do what Dave suggested and jumper the power pins to the pump with the relay removed. Use at least 16 gauge wire with a 15a fuse. The ECM-B fuse is a 20a and the 15a would tell you right away if there's a problem with the pump circuit. The "choke" or cold start is controlled by the VCM (computer). Remember that the ECM-B fuse powers the fuel pump and the VCM.

So try this. Jumper the sockets to start the fuel pump. Start the engine. Just let it idle and don't drive it. See which fuse blows 1st. If the 15a inline jumper fuse blow's you've got a problem with the pump and/or wiring. If the ECM-B fuse blow's 1st there's a problem with the VCM or wiring.

Just a thought? Last time the fuel filter was changed? Also the fuel pump intake screen could be clogged..........Steve

GMMerlin · #12 08-25-2006, 07:26 AM

Replace the fuel pump!
And don't forget to check the connector at the tank.
When you remove the pump assembly, you will find the wires (inside the tank to the pump) have the insulation burned off of them and are touching.

ricnor · #13 08-25-2006, 06:45 PM

Well jumppered the relay as you said and the fuse blew on contact, tried another one and the pump started, ran the motor and all was well, nothing happened so as it was now normal running temperature I decided to put the relay back in to see what happened, ran for a while and then stopped. Took relay out and put in jumper again and the fuse blew and blew and blew. So have WD40'ed everything at the back in readiness for tank removal tomorrow and see what the pump looks like. If pump looks ok I was going to run a new cable from front to back just to see if that makes a difference.
Will the burnt wires on the pump be obvious? (may sound a silly question but I have never seen a pump from within a fuel tank before).
As for filter change? I've had the truck for about 8000 miles and it is reading 98000 miles on the clock. I would assume that the filter hasn't been changed so will order one anyway just to know that it has been done.

Blue Bowtie · #14 08-25-2006, 10:39 PM

With a resonably close inspection, the overheated connectors should be relatively apparent:

Old Dave · #15 08-26-2006, 06:54 PM

Some of the new fuel pumps (Carter brand) come with the new harness from the pump to the top plate of the assembly. I bought mine at Car Quest which was their own brand made by Airtex. The pump did not come with the harness but I bought it seperately so I would have it when I did the job. My harness was closely inspected by me and it looked fine and everything was tight so I returned the harness ($12). In your situtation I would get the harness and the pump and put in regradless if it looks bad or not.

BTW where the locking ring was on mine on the top of the tank, was sealed up to keep moisture and dirt out. I started cleaning it off and discovered it was bee's wax (very sticky). I sealed it back up with bees wax from a new toilet ring that I had in the garage.

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